Gallium nitride based materials have a wide bandgap and high saturation electron velocity. For this reason, they are desirable materials for high-speed electronic devices such as field effect transistors (FET) and heterojunction bipolar transistors (HBT) as well as for blue light emitting devices.
It is important to form p-type and n-type conducting layers with high controllability for implementing light emitting devices and electronic devices. For gallium nitride based semiconductor materials, an n-type conducting layer can be formed by using silicon (Si) for n-type impurity. In contrast, while magnesium (Mg) or zinc (Zn) is used for p-type impurity, they have a low activation rate because of their deep impurity level. In addition, in the crystal growth based on the metal organic chemical vapor deposition (MOCVD) method used for growing a gallium nitride based crystal, hydrogen atoms resulting from the decomposition of hydrogen used in a carrier gas are combined with magnesium to form Mg—H, thereby deactivating magnesium.
As a method for increasing the magnesium activation rate, there is disclosed a technique of postprocessing based on electron beam irradiation (H. Amano et al., Jpn. J. Phys. 28 (1989) L2112) and heat treatment (S. Nakamura et al., Jpn. J. Appl. Phys. 31 (1992) 1258).
As another method of increasing the magnesium activation rate, there is disclosed a method of using an inert gas as a carrier gas during growth (JP 8-325094A (1996)).